This invention relates to hybrid manufacturing techniques, and more particularly to improved method and apparatus for soldering lead frames to conductive lands on hybrid substrates already having components soldered thereto.
A hybrid circuit assembly is essentially an electrical circuit formed on a dielectric substrate. It generally comprises a rectangularly shaped glass-ceramic substrate having resistors, electrically conductive circuit patterns, and conductive lands formed on the front side thereof; with other circuit elements being soldered to selected points on the patterns and leads being soldered to the lands which are located adjacent to one edge of the substrate. A prior-art technique of producing such a hybrid circuit assembly is to form the patterns, lands and resistive elements on the substrate, and then press fingers of a lead frame over the one edge of the substrate and associated lands. The base or bar on the lead frame is clamped in a holder of a rotary dipping convey machine such as the model RHV-360 sold by Hollis Engineering, Incorporated, of Nashua, N.H., under the trademark Acculine. The machine rotates the substrate 180.degree. in the vertical plane, and then completely immerses the entire hybrid and the lead frame in flux and molten solder to attach leads to lands and tin the circuit patterns. Components are then set out on the pre-soldered substrate and passed through a reflow solder operation to solder them to the circuit patterns. An alternate technique is to solder electrical components to patterns on the substrate prior to attaching leads thereto. After an operator presses lead frame fingers over the one edge of a substrate and adjacent lands, a clothespin is snapped onto the substrate. The clothespin is held by hand as an operator hopefully dips only the lead frame, substrate one edge and lands into molten solder. Since such a hand operation is done with individual substrates, it is time consuming and fatiguing to an operator. It is also unreliable in that when a substrate is misaligned in the solder or held there for too long a time interval, then components already soldered to the substrate may fall off or be moved out of alignment with the circuit patterns.
An object of this invention is the provision of improved method and apparatus for soldering leads to hybrid substrates.